1. Field of the Invention
The invention pertains to the field of block and tackle window balances. More particularly, the invention pertains to a block and tackle window balance which provides a sash mounted in a window frame with extended range of travel.
2. Description of Related Art
Typical hung window assemblies feature at least one moveable window sash mounted in a window frame. The sash slides up and down in the frame and is provided with a window balance of some type to counter the weight of the sash so that it can be easily moved up and down by the user. A popular configuration for window balances in this type of window uses a combination of springs and pulleys mounted in an elongate channel member to counterbalance the weight of the sash. The channel member has a generally “U” shaped cross-section for most or all of its length and can be mounted to the frame with a cord end attached to the sash. Alternately, as is the case in the embodiments related to this invention, the channel can be attached to the sash while the cord extends from the pulley elements in the channel via a pulley/roller at the lower end of the channel to connect to a side of the jamb above this “bottom” pulley/roller. (A jamb mounting hook positioned at the end of the cord is used to connect the cord to the jamb). However, in the latter embodiment, the range of travel of the sash in the frame is limited by the positioning of the bottom pulley/roller in the channel, which can interfere with the jamb mounting hook.
For ease of egress from the window in emergencies (and as a general matter of convenience) it is desirable for the window sash to have maximum upward travel in the window frame. This can be accomplished, and the problem of interference between the bottom pulley/roller and the jamb mounting hook alleviated, by moving the bottom pulley/roller for the jamb mounting hook closer to the lower end of the channel member. However, the upper and lower ends of the channel are usually taken up by, respectively, top and bottom guides that are attached to the channel and assist in connecting the channel to a window sash. This problem led to the initial attempted solution by U.S. Pat. Nos. 6,598,264 and 6,877,187; and application Ser. No. 11/029,074. The aforesaid patents and applications teach a system where a “bottom roller” is mounted in the bottom guide, combining the functions of these two parts. This does, in fact, serve to move this bottom roller closer to the end of the channel and create a system with greater travel. However, it leads to additional problems.
It is desirable in the window industry for parts to be as interchangeable as possible. Thus, in the prior art block and tackle window balances discussed it was not unusual to have systems where the tensioned elements (such as the springs, middle carriage assembly, cord, and end carriage assembly with bottom pulley) were mounted directly to the channel which could be stocked and/or stored as a stable assembly. This assembly could then be joined to different top and bottom guides as needed to fit different types, sizes and configurations of windows. However, this is no longer possible and/or is extremely limited by the types of configurations taught in U.S. Pat. Nos. 6,598,264 and 6,877,187; and in application Ser. No. 11/029,074. In these configurations, the bottom guide is included among the tensioned parts due to the fact that the bottom roller is mounted therein. Thus, it must be pre-mounted to the channel along with the other tensioned parts, limiting the ability of the channel to be used for multiple window types and severely limiting the usefulness of the channel as an interchangeable part.